Texture that only effects faces that are facing upwards
Use this node setup for your material:



The dot product of the face normal with vector (0, 0, 1) is 0 when the face normal is orthogonal (= horizontal) and maximal when equal. When pointing downwards the dot product is negative.

With the color ramp you can control the angular tolerance. If you don't want to have a smooth transition between texture and green you can move white handle to the black one.

This is used as the factor of a Mix Shader mixing the texture with a green diffuse material.

Result: